The present invention is directed, in general to polishing pads for chemical mechanical polishing of semiconductor wafers and integrated circuits. More specifically, the invention is directed to a packaged polishing pad as well as a method of preparing or packaging a chemical mechanical polishing pad for polishing.
Chemical-mechanical polishing (CMP) is used increasingly as a planarizing technique in the manufacture of VLSI integrated circuits. It has potential for planarizing a variety of materials in IC processing but is used most widely for planarizing metallization layers and interlevel dielectrics on semiconductor wafers, and for planarizing substrates for shallow trench isolation.
The success of CMP, over other methods such as etchback; is due to the higher degree of wafer planarity that is achievable with the CMP technique since ever-increasing needs for miniaturization in electronic devices requires tighter wafer planarity tolerances. In CMP, a semiconductor wafer is polished using a repetitive, regular motion of a mechanical polishing wheel and a slurry which may contain a mixture of fine particles and chemical etchants. By placing the slurry between the polishing wheel and the wafer, unwanted material may be successfully removed with a high degree of planarity. To aid in the planarization process, the polishing wheel commonly employs a specialized polishing pad that may be made from felted or woven natural fibers such as wool, urethane-impregnated felted polyester, or various types of polyurethane plastic.
There are three critical consumable components in the CMP process. One is the abrasive liquid slurry. The abrasive liquid slurry""s composition must be altered, and special formulations must be produced for each different substrate being polished. Some substrates require a high pH to be activated for polishing, and other substrates need a more acid environment. Still other substrates respond best to silica abrasives, while others require alumina or titanium abrasive particles. The second critical consumable component in the CMP process is the polishing pad. It must be very flat, uniform across its entire surface, and resistant to the chemical nature of the slurry and have the right combination of stiffness and compressibility to minimize effects like dishing and erosion. A third critical consumable component in the CMP process is the carrier film. The carrier film attaches the wafer to its rotating holder, must have an adequately flat and uniform in its thickness, must have an adhesive that will hold it tightly to the carrier but not too tightly to the wafer, all while being immune to the chemical environment in which it works.
One problem facing currently employed technologies is the degradation of the polishing pad material due to the chemically aggressive nature of the polishing slurry. Thus, the slurry chemistries cause the polishing properties to change drastically as the polishing process progresses, especially during initial exposure of the pad to the slurry. Rapidly changing polishing properties of the polishing pad are undesirable because control of the polishing""s effect on the wafer is lost.
To address this problem, a technique called xe2x80x9cseasoningxe2x80x9d has been adopted. A conventional seasoning approach involves exposing the pad to a conditioning-polishing environment. The pad is attached to a plate, and in the presence of a conditioning slurry, a conditioning ring is used to condition the pad. During this conditioning process, a force is applied to the conditioning ring that mechanically forces the slurry into the pad. The pad is thereby seasoned or conditioned for actual semiconductor wafer processing. The pad is typically seasoned in this fashion for 30 minutes to 120 minutes. While this traditional seasoning technique is somewhat helpful, these prior art processes still suffer from certain disadvantages. For example, even after a pad is conventionally seasoned as mentioned above, the pad properties can continue to change, thereby affecting the quality of the wafer""s polished surface.
Accordingly, what is needed in the art is method of preparing a polishing pad that does not suffer from the disadvantages associated with the prior art processes.
To address the deficiencies of the prior art, the present invention, in one embodiment, provides a method of preparing a polishing pad suitable for chemical mechanical polishing of a semiconductor wafer. In this embodiment, the method includes providing a polishing pad having a hygroscopic absorbency, soaking the polishing pad with an aqueous medium for a time sufficient to equilibrate the pad to prior to polishing with the pad, and placing the polishing pad on a polishing platen subsequent to the soaking.
In another embodiment the present invention provides a method of packaging a polishing pad for use in polishing a semiconductor wafer. This particular embodiment includes placing a polishing pad in a container configured to retain an aqueous medium therein, placing an aqueous medium in the container in a quantity sufficient to allow the polishing pad to equilibrate, and sealing the container.
Yet another embodiment provides a packaged polishing pad, comprising a sealable moisture tight package having a dimension sufficient to contain a polishing pad therein and a polishing pad soaked in an aqueous medium and located within the sealable moisture tight package.
The foregoing has outlined preferred and alternative features of the present invention so that those skilled in the art may better understand the detailed description of the invention that follows. Additional features of the invention will be described hereinafter that form the subject of the claims of the invention. Those skilled in the art should appreciate that they can readily use the disclosed conception and specific embodiment as a basis for designing or modifying other structures for carrying out the same purposes of the present invention. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the invention in its broadest form.